Imprisoned - constant time in the finish (7)
I believe the answer is:
encaged
'imprisoned constant time in the finish' is the definition.
I can't judge whether this definition defines the answer.
'constant time in the finish' is the wordplay.
'constant' becomes 'c' (mathematical abbreviation).
'time' becomes 'age' (an age is a period of time).
'in' means one lot of letters goes inside another.
'the finish' becomes 'end' (I've seen this before).
'c'+'age'='cage'
'cage' going inside 'end' is 'ENCAGED'.
Can you help me to learn more?
(Another definition for encaged that I've seen is " put behind bars".)